The present invention pertains to a technical field of a seat belt retractor which is installed in a vehicle for transportation such as an automobile, an airplane, or a ship (hereinafter, collectively referred to as “vehicle”) and which winds up a seat belt for restraining and protecting an occupant by means of a motor and a seat belt device using the same, more particularly, to a technical field of a seat belt retractor in which the winding of a seat belt is performed efficiently by a motor using limited power consumption and a seat belt device using the same.
Conventionally, a seat belt device installed in a vehicle such as an automobile comprises at least a seat belt retractor for winding up a seat belt, a tongue slidably supported to the seat belt, and a buckle to which the tongue can be latched. In the event of emergency such as a vehicle collision at which large deceleration is exerted on the vehicle while an occupant wears the seat belt in a state that the tongue is latched to the buckle, the seat belt device prevents the occupant from jumping out of a vehicle seat by restraining the occupant with the seat belt, thereby protecting the occupant.
The seat belt device is provided with a seat belt retractor for winding up the seat belt. The seat belt retractor comprises a biasing means such as a spiral spring which always biases a spool, on which the seat belt is wound, in the belt-winding direction. When not used, the seat belt is fully wound on the spool by the biasing force of the biasing means. When used, the seat belt is withdrawn against the biasing force of the biasing means and is worn by the occupant. In the seat belt retractor, a locking mechanism is activated in the event of emergency as mentioned above to stop the rotation of the spool in an unwinding direction, thereby preventing the seat belt from being withdrawn. Therefore, the seat belt can securely restrain and thus protect the occupant.
By the way, as one of conventional seat belt devices as mentioned above, a motorized seat belt retractor has been proposed in which, when it is determined that the collision is unavoidable before a vehicle collision, the tension on a seat belt is increased by increasing the driving force of a motor to wind up the seat belt, thereby increasing the restraint force of the occupant and, when the vehicle collision is actually detected, a gas generator for a pretensioner is actuated to generate gas whereby the seat belt is rapidly wound up by the generated gas, thereby further increasing the restraint force for the occupant, as disclosed in Japanese Patent Unexamined Publication 2000-95064 (which is incorporated by reference herein in its entirety).
On the other hand, a seat belt retractor has been also proposed in which, as the power transmission passages for transmitting the rotational torque of the motor, a first power transmission passage for transmitting the rotational torque of a motor to the biasing means as mentioned above to increase the force of the biasing means and a second power transmission passage for transmitting the rotational torque of the motor to the spool at a fixed speed reduction ratio are provided wherein the first power transmission passage is selected by the actuation of a first solenoid and the second power transmission passage is selected by the actuation of a second solenoid, thereby controlling the belt tension, as disclosed in Japanese Patent Unexamined Publication 2000-177535 (which is incorporated by reference herein in its entirety).
By the way, there are various modes of winding up the seat belt such as a mode for rapidly winding up the seat belt for removing slack of the seat belt or for the storage and a mode for winding up the seat belt with large rotational torque for restraining the occupant. The rotational speed of the spool and the belt winding torque on the spool differ according to the mode of winding up the seat belt.
However, in the seat belt retractor disclosed in the aforementioned Japanese Patent Unexamined Publication 2000-95064, the power transmission mechanism transmitting the driving force of the motor to the spool has only one power transmission passage of a fixed speed reduction ratio. Accordingly, the fixed speed reduction ratio is uniquely determined so that it is difficult to flexibly and effectively correspond to the various rotational speed of the spool and the various belt winding torque on the spool.
It is considered, as a way to comply with this, to sensitively control the rotational speed of the motor and the winding-up force of the spool. However, such sensitive control not only makes the control of the motor difficult but also increases the power consumption. It is required to increase the rotational torque of the motor in order to obtain large restraining force in the event of emergency such as a vehicle collision. To increase the rotational torque of the motor, the power consumption must be so large or the size of the motor must be so large.
On the other hand, in the seat belt retractor disclosed in the aforementioned Japanese Patent Unexamined Publication 2000-177535, one power transmission passage is provided for transmitting the rotational torque of the motor to the aforementioned biasing means to control the biasing force of the biasing means, while the other power transmission passage is provided for directly transmitting the rotational torque of the motor to the spool to directly control the winding-up force of the spool by the rotational torque of the motor. Though the seat belt retractor disclosed in Japanese Patent Unexamined Publication 2000-177535 has, as the power transmission passages, two different power transmission passages of different speed reduction ratios, there is only one power transmission passage of a fixed speed reduction ratio for the purpose of directly transmitting the rotational torque of the motor to the spool. Accordingly, similarly to the case of the aforementioned Japanese Patent Unexamined Publication 2000-95064, the fixed speed reduction ratio is uniquely determined for directly transmitting the rotational torque of the motor to the spool so that it is difficult to flexibly and effectively correspond to the various rotational speed of the spool and the various belt winding torque on the spool.
Though the belt winding force can be controlled at some level by controlling the biasing force of the biasing means with the rotational torque of the motor so as to control the belt winding force of the spool according to the controlled biasing force, it is preferable to sensitively control the winding force of the spool by effectively utilizing the rotational torque of the motor.